1. Technical Field
The invention relates to a non-reciprocal component comprising a ferrite substrate having a first and an opposing second side located on a ground layer, wherein a first metal line and a second metal line are located on the ferrite substrate in parallel to each other. The invention relates further to an integrated circuit including a non-reciprocal component and to a circulator.
2. Description of the Related Art
Non-reciprocal components are used especially in microwave technology, which has become very important during the last years. Various frequency bands are used for commercial applications, e.g., GSM (˜1 GHz), UMTS (˜2 GHz), Bluetooth (˜2.5 GHz), WLAN (˜5 GHz) etc. There is a clear trend towards higher frequencies in order to obtain larger bandwidths and hence higher data rates. Moreover new microwave applications at higher frequencies like car radar (24 GHz or 77 GHz) have entered the market. In this sector, a large growth within the next few years is expected.
Non-reciprocal RF components like circulators and isolators have a wide range of applications. In many cases simple and robust system architectures can be used using such non-reciprocal RF components. The application of non-reciprocal RF components simplifies the design process of high frequency parts and saves cost. E.g., isolators are used in the RF front end of UMTS phones, since the required linearity of the receiver can be guaranteed in a simple way. In that case the isolator is connected between an antenna of a mobile terminal and an output power amplifier. So a signal coming from the output power amplifier is coupled into the isolator in port 1 and outputted at port 2 and directed to the antenna. The isolator insulates the power amplifier from a signal running back from the antenna to the power amplifier. The high cost of the isolator is accepted, since a modified system architecture which does not need an isolator would be very difficult to design and not reliable.
The high production costs of state of the art non-reciprocal RF components are due to their very complex internal set up. To generate the non-reciprocal effect, ferrite material is essentially needed. Apart from a ferrite material various metal electrodes or metallization layers are required to guide the microwave, wherein the microwave is guided between metallization layers. One or two permanent magnets are needed to magnetize the ferrite material. Moreover several pole pieces are needed to guide the magnetic field lines of the permanent magnet in order to generate a very homogeneous magnetic field in the region of the ferrite material. All parts of the non-reciprocal component have to be assembled during a complicated production process.
The integration of passive components like capacitors and inductors either into the substrate by using multilayer LTCC or multilayer laminates, etc. or directly on a semiconductor chip has become an industrial standard in order to miniaturize and reduce the costs of electronic circuits. Unfortunately, integrated solutions for non-reciprocal RF components are up to now not available.
Since the common design of the non-reciprocal RF components uses a magnetic field, which is directed perpendicular to the propagation direction of the microwave, it was not possible to integrate such components, particularly because the permanent magnets have to be placed below and/or above the ferrite material. This results in a large height of the component. Since the required permanent magnetic field increases with the working frequency, the height problems become particularly severe in the high frequency range. Moreover, the configuration using a perpendicular magnetic field leads to large demagnetization effects, which can be compensated only by using stronger and therefore bigger permanent magnets. At high working frequencies, this problem becomes more and more pronounced. Integration of such a design is therefore not feasible.
A better configuration with respect to integration of passive components would be realized if the direction of the magnetic field is parallel or in-plane to the ferrite substrate. This means the magnetic field lines are directed in a propagation direction of the microwave. However, non-reciprocal components, which utilize this in-plane magnetization, are not available.
The simplest design of this in-plane magnetization of the ferrite substrate may include two parallel striplines or microstrip lines, which are printed on a ferrite substrate. To achieve an acceptable non-reciprocal behavior of the components using in-plane magnetization of the ferrite substrate, a large length of the metal lines will be required. The required length of the metal lines would reduce the commercial value of the design.